DESCRIPTION: In previous work, the Investigator found that rats deprived of calcium have a robust and very specific appetite for sodium, and that corticosterone (a glucocorticoid hormone) may be an important mediator of the phenomenon. He now proposes characterizing the role of glucocorticoids in sodium appetite. Specific experiments will determine the contribution of corticosterone to the spontaneous sodium intake that occurs under "normal" conditions; the sodium appetite that occurs on a calcium-deficient diet; and several other paradigms in which high sodium intake is evinced (i.e., during dietary iron or protein deficiency; reproduction; restraint; or treatment with furosemide or angiotensin-II). For each model, corticosterone and/or RU-486 (a corticosterone antagonist) will be given and several behavioral and physiological parameters assessed.